The present disclosure relates to a display and a method of manufacturing the display, to an electronic apparatus, to a unit, and to a transfer printing method.
The present disclosure also relates to an organic electroluminescence (EL) unit that emits light by utilizing an organic EL phenomenon and a method of manufacturing the organic EL unit, and to an electronic apparatus.
Recently, it is proposed to form a light emitting layer (organic layer) of an organic EL display by a printing method. A printing method has advantages that process cost thereof is low and larger apparatuses are easily formed, compared to a vacuum evaporation method.
The printing methods are roughly classified into a non-contact type and a contact type. An ink jet method and a nozzle printing method is known as examples of the non-contact type method. These methods have advantage that larger apparatuses are easily formed and material use efficiency is high. However, in these methods, a bank (dividing wall) may be provided to define positions to apply ink, and a film thickness in a pixel may be uneven due to a factor such as wet of the ink on the bank.
On the other hand, a method such as a flexographic printing method, a gravure offset printing method, and a reverse offset printing method is known as examples of the contact type method. The flexographic printing method has advantages that thickness accuracy on a substrate is relatively high, time necessary for printing is short, and a printing machine is allowed to be larger. However, the flexographic printing method has low plate accuracy and is difficult to be employed for higher-definition or larger-sized displays. The gravure offset printing method has high plate accuracy and may be employed for higher-definition or larger-sized displays. However, film thickness distribution in a pixel is of a mound shape and light emission luminance may be uneven.
The reverse offset printing method has attracted attention in this circumstance. In the reverse offset method, a transfer member on which ink is uniformly deposited is pressed onto a plate to remove ink on non-printing portions, and then, a pattern remained on the transfer member is transferred to a member to be printed as a transfer pattern. This reverse offset printing method achieves more-uniform film thickness distribution and high-definition patterning.
Therefore, the reverse offset printing method is expected to be applied not only to printing of a light emitting layer of an organic EL display but to a whole field of a so-called printed electronics. Specifically, it is considered to apply the reverse offset printing method to printing of, for example, wiring and insulation patterns of a printed board, photoresists used in photolithography processes, color filters for displays, and organic layers of organic thin film transistors (TFTs). For example, Japanese Unexamined Patent Application Publication No. 2010-158799 discloses an example of a technology that uses such a reverse offset method.
Further, a display device with high performance has been demanded in accordance with accelerated development of information communication industry. In particular, an organic EL device that has attracted attention as a next-generation display device has advantages that a viewing angle is wide and contrast is favorable as a self-emitting display device, and also response time is short.
The organic EL device has a configuration in which a plurality of layers including a light emitting layer are laminated. The layers may be formed, for example, by a vacuum evaporation method. Specifically, a layer of a desired shape is patterned by sandwiching a mask with an opening between an evaporation source and a substrate, in a typical method. When a display that uses such an organic EL device is formed in larger size or in higher definition, for example, the mask may be bent and carrying of the components may be complicated. Therefore, alignment may be difficult and opening ratio decreases. Accordingly, performance of the device is lowered.
On the other hand, for example, Japanese Unexamined Patent Application Publications Nos. 1997-167684 and 2002-216957 disclose a method of fabricating a pattern by thermal transfer. However, this method uses a laser as a heat source, and therefore, large cost is necessary for the manufacturing apparatus as a whole.
Therefore, a reverse printing method has been proposed that uses a silicon-rubber blanket (hereinafter, simply referred to as “blanket”), as a method of fabricating a high-definition display by low-cost manufacturing process, (for example, see Japanese Unexamined Patent Application Publications Nos. 2007-95517, 2007-90698, and 2010-58330). In the reverse printing method, ink that includes a light emitting material is applied onto a blanket, and then, an unnecessary region (non-printing pattern) of the ink layer is selectively removed with use of a recessed plate. A light emitting layer is formed by transfer with use of the blanket on which a printing pattern is formed as described above.
Moreover, it is important to allow the film formed on the blanket to retain appropriate humidity in order to obtain a favorable pattern by such a reverse printing method. Japanese Unexamined Patent Application Publications Nos. 2007-95517 and 2007-90698 disclose that a blanket is swollen with a solvent included in ink when the ink is applied onto the blanket.